Polyphenylene polymer of various structural types is known. Linear polyphenylenes may be of the rigid-rod type as disclosed in U.S. Pat. No. 5,227,457, semi-rigid as disclosed in U.S. Pat. No. 5,886,130, and may have reactive side groups as disclosed in U.S. Pat. No. 5,625,010 or end groups as disclosed in U.S. Pat. No. 5,670,564, the entire contents of which patents are incorporated herein by this reference. Polyphenylenes may also have a branched (Kovacic et al., Chem. Rev., 1987, 87, 357-379), or hyperbranched (Kim et al., Macromol., 1992, 25, 5561-5572) structure.
The backbone of polyphenylene polymers is very strong and chemically and thermally inert. If other repeat units or side groups incorporated into polyphenylene are also strong and inert the polymer as a whole will exhibit these properties. The polyphenylene backbone also has a low dielectric constant, low affinity for water, and a high refractive index. These features are desirable for a wide variety of products, including films, fibers, molded and extruded parts, coatings, foams, and composites.
Linear polyphenylenes suffer from low solubility and are generally difficult to process. Selection of appropriate side groups, as in U.S. Pat. Nos. 5,227,457 and 5,886,130, is essential for practical levels of solubility and for melt processability. Inclusion of branch points also may aid solubility and processability; however, previous branched polyphenylenes either have been prepared from costly and/or unstable monomers (e.g. diethynylbenzenes) or have had uncontrollable levels of branching.
Hyper-branched polyphenylenes have controlled amounts of branching; however, they are, by design, maximally branched. Hyper-branched polymers have some interesting properties but, unlike linear and lightly branched polymers, do not entangle and are therefore poor film formers and are generally brittle when molded.
It would be desirable to have polyphenylene polymers with all of the above mentioned positive attributes, including high strength, low dielectric constant, low water uptake, chemical and thermal stability, easy processibility into tough films, fibers, foams, molded parts and the like, and low cost. An improvement in the art would be a polyphenylene material with a controllable degree of branching, thus providing a means for improving solubility and processibility.